Chapter 14: Nervous Tissue SYDNEY Flashcards
what is the nervous system?
the body’s primary communication and control system
functions of the nervous system
-monitor changes: inside and outside, sensory input
-process and interpret
-causes a response: motor output, effector organs
for convenient organizational purposes, what two categories is the nervous system divided into?
-structural
-functional
types of structural nervous systems
-central nervous system (CNS)
-peripheral nervous system (PNS)
types of functional nervous systems
-sensory nervous system
-motor nervous system
what parts of the body are included in the CNS?
-brain
-spinal cord
how is the brain protected in the CNS?
protected and enclosed within the skull
how is the spinal cord protected in the CNS?
housed and protected within the vertebral canal
what are the two types of nerves that are included in the PNS?
-cranial nerves: 12 (nerves that extend from the brain)
-spinal nerves (nerves that extend from the spinal cord)
-ganglia
what is ganglia
clusters of neuron cell bodies located outside the CNS
the sensory motor system and motor nervous system both perform three general functions:
-collect information
-process and evaluate information
-initiate response to information
what happens when information is collected?
specialized PNS structures called receptors detect changes in the internal or external environment (stimuli) and pass them on to the CNS as sensory input
what happens during process and evaluating information?
after processing sensory input, the CNS determines what, if any, response is required
what happens during the initiating response to information?
the CNS initiates specific nerve impulses called motor motor output. motor output travels through structures of the PNS to effectors
the sensory nervous system is subdivided into:
-somatic sensory
-visceral sensory
function of somatic sensory system
sensory input that is voluntarily perceived from receptors
what are the somatic sensory components?
general somatic senses: touch, pain, pressure, vibration, temperature, and proprioception (sensing position or movement of joints and limbs)
special senses: taste, vision, hearing, balance, smell
function of visceral sensory system
sensory input that is involuntarily perceived from receptors of blood vessels and internal organs
what are the visceral components?
components transmit nerve impulses from chemical compostion of blood to the CNS
types of neurons in the sensory nervous system
afferent neurons
what does the term afferent mean?
-inflowing
-indicating that nerve impulses are transmitted to the CNS
types of neurons in the motor nervous system
efferent neurons
what does the term efferent mean?
-conducting outward
-indicating that nerve impulses are transmitted from the CNS
what is the sensory nervous system responsible for?
receiving sensory information from receptors and transmitting this information to the CNS
what is the motor nervous system responsible for?
transmitting motor impulses from the CNS to effectors (muscles or glands)
the motor nervous system is subdivided into:
-somatic nervous system (SNS): voluntary
-autonomic nervous system (ANS): involuntary
function of somatic nervous system
motor output that is voluntarily controlled; effector is skeletal muscle
function of autonomic nervous system
motor output that is involuntarily controlled; effectors are cardiac muscle, smooth muscle, and glands
components of autonomic nervous system
sympathetic and parasympathetic components
basic structural unit of the nervous system
neuron
functions of the neuron
-excitable cell
-long-lived
-high metabolic rate
-regeneration: unable to divide
what does the excitable cell mean?
generate, send, and receive nerve impulses
characteristic of the high metabolic rate
neurons survival depends upon continuous and abundant supplies of oxygen & glucose
structure of a neuron
-soma: cell body
-dendrites: processes that branch off the cell body
-axon: process extending from the cell body to make contact with other neurons, muscle cells or gland cells
processes (extensions) of neuron structures
-dendrites
-axon
-telodendria
-synaptic knobs
function of the soma
-serves as the neuron’s control center and is responsible for receiving, integrating, and sending nerve impulses
-includes nucleus
-machinery
length, feature, and function of dendrites
-shorter
-dendritic spines
-impulses to cell body
number, function, and feature of axon
-one or none
-impulse away from soma
-axon hillock: triangular region connecting cell body to axon
what is telodendria? function?
-fine terminal branches of an axon or axon collateral (side branches of an axon)
-transmitting signals to other neurons or target cells
what are synaptic knobs?
slightly expanded regions at the tips of the telodendria
function of synaptic knobs
meet other neurons
neurons are classified structurally into three types, based upon the number of neuron processes extending from the cell body:
-unipolar (aka pseudounipolar) neurons
-bipolar neurons
-multipolar neurons
what is a unipolar neuron?
it has a single process that divides into a peripheral process and a central process
features of unipolar neurons
-single-short neuron processes, branches like a T
-long axon
-function: detect stimuli in the form of touch, pressure, temperature, or chemicals
-location: cell bodies (posterior root ganglia - spinal nerves)
example of unipolar neuron
sensory neurons
What is a bipolar neuron?
-it has two processes that extend from the soma: one axon and one dendrite
-uncommon in humans
special senses of the bipolar neurons
-olfactory epithelium of nose
-retina of eye
what is the multipolar neuron?
-multiple processes: many dendrites and a single axon extend from the soma
-most common type
example of multipolar neuron
motor neurons that innervate muscle and glands
Four types of glial cells occur in the CNS
-astrocytes
-ependymal cells
-microglial cells
-oligodendrocytes
all glial cells, except microglia, are derived from ______
neural ectoderm
what are microglia derived from?
stem cells within the red bone marrow that become monocytes (a type of white blood cell)
what are glial cells? function of glial cells?
-occur within both the CNS and the PNS
-Abundance: outnumber neurons
-fun fact: cause of all tumors in nervous system
-function: assist neurons
how do glial cells assist neurons?
-physically protect
-nourish
-provide framework
Location and description of astrocyte
-location: CNS
-Description: Large cell with numerous cell processes; in contact with neurons and capillaries; most common type of glial cell
functions of astrocytes
-blood-brain barrier
-fluid composition
-regulate synaptic pathways
-structural support
-fill space of dead neurons
-assist neuron development in the fetus
how do the astrocytes assist neural development in the fetus?
they help direct the development of neurons in the fetal brain by secreting chemicals that regulate the connections between neurons
what are the ependymal cells?
cuboidal epithelial cells that line the internal cavities of the brain and the central canal of the spinal cord
significance of cilia on ependymal cells
they have cilia on their apical surfaces that help circulate the CSF (cerebrospinal fluid)
how is the choroid plexus formed?
ependymal cells and nearby blood capillaries together form a network call the choroid plexus
choroid plexus produces cerebrospinal fluid. what is CSF?
a clear liquid that bathes the CNS and fills its internal cavities
what are microglial cells?
small cells that have slender branches extending from the main cell body
features of microglial cells
-rare: low as 5%
-mobile: wander through the CNS and replicate in response to infection
-perform phagocytic activity and remove debris from dead/damaged nervous tissue
what do the microglial cells resemble?
macrophages of the immune system
what are oligodendrocytes?
-large cells with a bulbous body and slender cytoplasmic extensions or processes
-myelinate CNS axons
-many neurons
protective covering around the axon
myelin sheath
what is the myelin sheath made of?
many overlapping layers of plasma membrane
what is the glial cell type in the PNS?
neurolemnocytes/ Schwann cells
shape of Schwann cells
-elongated, flattened cells that wrap around the axons within the PNS, insulating the axon and forming a myelin sheath (1 mm per cell)
-one neuron
in the CNS, a myelin sheath forms from ?
oligodendrocytes
in the PNS, a myelin sheath forms from ?
shwann cells
what are the small spaces called that interrupt the myelin sheath between adjacent oligodendrocytes or shwann cells?
neurofibril nodes/nodes of Ranvier
features of neurofibril nodes
-no sheath
-voltage change
what is the process of the nerve impulse jumping from neurofibril node to neurofibril node in a myelinated axon?
saltatory conduction
what is the process of the nerve impulse traveling the entire length of the axon membrane in an unmyelinated axon?
continuous conduction
difference between saltatory conduction and continuous conduction?
saltatory conduction is faster and less energy
continuous conduction takes longer to reach end of the axon
what is a synapse?
junction between an axon and another cell
a typical synapse in the CNS consists of the close association of a
presynaptic neuron and postsynaptic neuron
what is a synaptic cleft?
very narrow gap between presynaptic neuron and postsynaptic neuron
common type of synapse
axodendritic synapse
Why does axodendritic synapse occur?
occurs between the synaptic knobs of a presynaptic neuron and the dendrites of the postsynaptic neuron
most numerous type of synapse
chemical synapse
function of chemical synapse
facilitates most of the interactions between neurons and all communications between neurons and effectors
what is a neurotransmitter?
-chemical messengers
where are the neurotransmitters released from?
-presynaptic cell only
-then bind to receptor proteins found only in the plasma membrane of the postsynaptic cell
sequence of events of synapse:
- incoming impulse
- calcium comes in
- synaptic vesicles move to membrane
- neurotransmitter released
- Na+ (sodium ions) channels open on postsynaptic cell
- new impulse
- enzymes in synaptic cleft clear neurotransmitter
